1. Field of the Invention
The present invention relates to a lens drive device which drives an optical system equipped with multiple lenses. More particularly, the present invention relates to a lens drive device which drives a zoom optical system.
2. Description of the Related Art
A number of conventional devices perform variable power operations and focusing operations in zoom optical systems. For example, Japanese Laid Open Patent Publication No. SHO 60-122931 ("the '931 publication") and Japanese Laid Open Patent Publication No. SHO 61-259210 ("the '210 publication") describe devices which perform the above operations while using a single drive source. In the '931 publication, the focal length is changed by inserting a supplementary optical system into the optical path of the main optical system while varying the focal length of the main optical system. The entire optical system is then driven in the direction of the optical axis to adjust focus for a set focal length.
In the '210 publication two lens groups are installed in a common cam cylinder. The cam cylinder is then set so that a variable power operation and a focusing operation occur in the two lens groups when the cam cylinder is continuously rotated in one direction. The focusing operation aligns the focal plane of the optical system for a desired subject with a specified position. The variable power operation changes the focal length of the optical system.
In the aforementioned conventional devices, because all lens groups are driven during the focusing operation, the required lens drive is large and the required drive time is long. Additionally, a larger lens barrel is required. In the case of the '210 publication, a need for cam cylinder adjustment requires a larger diameter lens barrel. Moreover, change between the variable power range and the focusing range require that a cam groove be changed when a cam is used. Accordingly, the shape of the cam groove becomes complicated thereby increasing manufacturing time and labor.